List files with two dots in their names using java regular expressions

Question

I was trying to match files in a directory that had two dots in their name, something like theme.default.properties
I thought the pattern .\\..\\.. should be the required pattern [. matches any character and \. matches a dot] but it matches both oneTwo.txt and theme.default.properties

I tried the following:
[resources/themes has two files oneTwo.txt and theme.default.properties]
1.

public static void loadThemes()
{
    File themeDirectory = new File("resources/themes");
    if(themeDirectory.exists())
    {
        File[] themeFiles = themeDirectory.listFiles();
        for(File themeFile : themeFiles)
        {
            if(themeFile.getName().matches(".\\..\\.."))
            {
                System.out.println(themeFile.getName());
            }
        }
    }
}

This prints nothing

and the following

File[] themeFiles = themeDirectory.listFiles(new FilenameFilter()
{
    public boolean accept(File dir, String name)
    {
    return name.matches(".\\..\\..");
    }
});

for (File file : themeFiles)
{
    System.out.println(file.getName());
}

prints both

oneTwo.txt
theme.default.properties

I am unable to find why these two give different results and which pattern I should be using to match two dots...

Can someone help?

Answer 1

This will return true if the filename has two dots in its name, separated by word characters:

matches("\\w+\\.\\w+\\.\\w+")

Matches the following:

aaa.bbb.ccc
aaa.bbb.ccc
111.aaa.bbb
aaa.b_b.ccc
a.b.c

Does not match the following:

aaa.bbb
..
.
---.aaa.bbb
aaa.bbb.ccc.ddd
a-a.bbb.ccc

Answer 2

I cannot reproduce your findings.

After removing the semicolon after the if in your first snippet, both versions print nothing for me. Both versions should print the same filenames, namely those that consist of

a single character, a dot, a single character, a dot, a single character

A test with an additional file named "a.b.c" prints that file.

If you want to match files containing exactly two dots, use the pattern

"[^.]*\\.[^.]*\\.[^.]*"

Answer 3

Another possibilities with less headache:

Replace everything which is not a dot and count the occurrences:

public boolean accept(File dir, String name) {
    return name.replaceAll("[^.]", "").length() == 2;
}

or split on any inner dot and count the parts:

public boolean accept(File dir, String name) {
    return name.split("\\.", -1).length - 1 == 2;
}